A typical fire damper includes a rectangular frame sized to fit closely within the duct, and a series of fire-resistant blades that are carried by the frame and pivotally coupled to one another so that they can adopt either a folded configuration at one side of the frame for normal air flow along the duct, or an extended configuration in which the blades form a curtain extending across and closing the duct in the event of fire. The blades are spring-biassed towards this extended configuration but are normally held folded by a fusible link assembly which melts and releases the blades when exposed to a predetermined elevated temperature.
The term "fire damper" as used in this application is intended to denote any damper of the general type described, which closes automatically in response to a predetermined elevated temperature.
Fire dampers of the general type described have been used satisfactorily for many years. For example, reference may be had to the present applicants' own U.S. Pat. No. 4,333,392 issued June 8, 1982. However, these types of dampers have generally been designed for one-time operation only and cannot conveniently be operated periodically for testing purposes. Many building codes now require that each fire damper in a building be examined and operated once a year to check that the damper is in operable condition. It is now considered that this procedure is important for all installations but is especially critical in schools, hospitals and nursing homes.